It is known that diketenes may be obtained by allowing at least equimolar quantities of triethyl amine to act on carboxylic acid halides containing at least one hydrogen atom in the .alpha.-position to the chlorocarbonyl group. The monomeric ketenes formed in situ stabilize spontaneously to form dimers, trimers and polymers whose structure is governed both by the type and number of substituents on the .alpha.-carbon atom of the carboxylic acid chloride (J. Amer. Chem. Soc. 87 (1965), 5191).
Reactions of ketenes prepared in situ with isocyanates, in which malonimides are formed, are also known (J. Org. Chem. 30 (1965), 2466).